1. Technical Field
This disclosed subject matter generally relates to devices and methods for treating veins and conditions related to veins. More particularly, the disclosed subject matter relates to devices and methods that are useful for treating venous anatomies to improve venous sufficiency.
2. Description of Background
Multiple Sclerosis (MS) is a debilitating disease in which the myelin surrounding the nerves is damaged, resulting in inhibition of nerve communication and impairment of physical and cognitive abilities. There is currently no cure for MS, but management of the disease has been advanced through the use of medical treatments, diet, and other non-surgical means. These treatments reflect the lack of a known cause of MS. MS sufferers apparently have a high prevalence of narrowing, twisting, or blockage of the veins that remove blood from the main extracranial cerebrospinal veins, the jugular, and the azygous venous systems. These abnormalities cause blood “refluxing”, or retrograde flow, which creates reflux in the central nervous system. As a result, pooling of non-oxygenated blood can occur along with pericapillary iron deposition. Since iron is known to create free radicals that are toxic to cells, it is hypothesized that the MS inflammations may be caused by these iron deposits as seen in CVD, mentioned above. The high iron content of MS patients' brains has been confirmed. The work led to the coining of the venous disorder Chronic Cerebrospinal Venous Insufficiency (CCSVI).
Veins are thin structures that lack some of the muscular features of arteries. Thus, distension of the veins is common. In the internal jugular vein, MS sufferers can develop distension and bulging as shown in FIG. 1. These bulbs can expand, or the entire length of vessel, or a substantial portion thereof, may expand, which causes blood accumulation and reflux as described above. Further, the venous system, and particularly the jugular portion of the venous system, includes valves that operate to allow blood to flow easily in one direction but resist the backflow of blood in the opposite direction. Veins can distend near the venous valves, and this distention can occur on either side of tile valve. For example, the vein may have a barbell shape with the valve in the handle area. Thus, the valve can act as a stenosis that restricts blood now in both directions and thereby inhibits now. Poor venous drainage and the resulting deposition of iron may be a primary or secondary cause of other diseases as well. For example, beyond MS, the treatment of CCSVI can also help prevent or treat dementia, Alzheimer's disease, or other diseases of the central nervous system.
There is a need for a method that can be used to reduce the bulbs or distension within a vein in order to reduce reflux and blood accumulation and thereby treat an underlying disease. There is also a need to maintain a venous valve open since blood now through the jugular veins can be beneficial, particularly in preventing pooling of blood in the brain.
Stenting is one option for treating CCSVI because a stent placed in the anatomy would eliminate the narrowing, twisting, or blockage of the veins, and thus prevent refluxing by allowing normal drainage of blood from the brain. Traditionally, cylindrical stents have been used in the treatment of vascular disease. That is, stents in their as-cut configuration are traditionally cylindrical. The reason for this is essentially twofold. First, the cost of manufacturing a non-cylindrical stent is substantially higher using traditional processes, and second, there has not been a strong demand for non-cylindrical stents since most diseased vessels are essentially cylindrical, and any anatomical deviations can be compensated for through balloon deployment and touch-up. However, there are no stents available on the market that are sized or designed for treating the vessel conditions relevant to CCSVI and the use of cylindrical stents to do so may not be fruitful.
Stenting abnormal vessel segments with traditional cylindrical stents has at least two downfalls. First, such stents have a tendency to dislodge from the vein because the veins have low radial force and are relatively large compared to typical stent diameters. When this happens, the stent may flow downstream and cause risk to the patient if it enters the heart, another organ, or otherwise disrupts blood flow, for example. Second, a stent with a cylindrical profile may not conform fully to a bulbous vein, and there may therefore be poor scaffolding and opportunity for thrombus formation in the gaps between the vein wall and the stent. Thus, there is a need for a stent that can be deployed within non-cylindrical vessel segments that provides the advantages of good vessel conformity in unusual anatomies, and that can produce an anchoring effect within a vein to prevent stent loss.
For many of the devices that may be used for the treatment of CCSVI, access to and delivery within the jugular vein may be necessary. However, as shown in FIG. 2, even basic access to a jugular can be difficult to accomplish without damaging the venous valves. As shown, the venous valves are formed by valve leaflets which are very thin structures that tend to protrude and taper in the antegrade direction. However, since access to the patient anatomy during interventional procedures is commonly made in the radial or femoral region, a guidewire will normally be passed in the retrograde direction. Therefore, as the guidewire is passed into the vein, it may tend to catch the valve leaflets and press against them in a resistive manner. Due to the relative weakness of the leaflets, they may tear or be otherwise damages. If the leaflets tear, they may be unable to resist backflow and therefore their function will be destroyed. This same problem can occur when other devices, such as balloon catheters or other catheter devices, are passed in the same direction as the guidewire. Thus, there is a need for a method and system of accessing the jugular veins that will eliminate or minimize the risk of damaging the valve leaflets.